The present invention relates to a method for discriminating the authenticity of a bill and an apparatus therefor for use in automatic vending machine, automatic service machine, automatic exchanger, automatic cash dispenser, etc.
An automatic vending machine or the like is required to discriminate the authenticity of a bill put into the machine. To this end, conventionally, the machine is equipped with an apparatus for discriminating the authenticity of a bill, which comprises, for instance, a light source for irradiating light onto the bill, and a light-receiving element for receiving reflected or transmitted light from the bill, and which operates to discriminate the authenticity of the bill on the bass of a level of an output of the light-receiving element. In another prior art (see, Japanese Provisional Patent Publication No. 62-296292), two color components of the reflected light are separately detected, so as to determine a color of the bill on the basis of respective detected levels of the two color components, to thereby discriminate the authenticity of the bill. A still another prior art is known (see, Japanese Provisional Patent Publication No. 62-276685), which is arranged to discriminate an authentic bill from a counterfeit bill obtained by color-copying the authentic bill on the basis of an output of a light-receiving element, which receives a regularly reflected light from a surface of a bill, and that of another light-receiving element which receives an irregularly reflected light therefrom.
However, on one hand, the light source and the light-receiving element change is their characteristics as an ambient temperature varies, and on the other hand, a thrown bill also includes variable factors such as freshness/oldness of the bill, presence/absence of wrinkles and stains in the bill. Accordingly, a difficulty is encountered in setting a reference level in case that discrimination of the authenticity of a bill is effected on the basis of an output of the light-receiving element. Namely, if the reference level is strictly set to a level close to the authentic-bill-side, an authentic bill is sometimes erroneously determined as a counterfeit bill. On the contrary, if the reference level is loosely set to a level close to the counterfeit-bill-side, a counterfeit bill can be erroneously determined as an authentic bill. In this manner, according to prior art, a difficulty arises in eliminating an incorrect discrimination. Particularly, it is difficult to accurately discriminate an authentic bill from a sophisticated counterfeit bill which is obtained by color-copying the authentic bill.